Multi‐wavelength Yb‐doped fiber‐ring laser

Abstract

A multi-wavelength ytterbium-doped fiber-ring laser is obtained using a spatial-mode beating filter, placing a section of a G.652 fiber sample into the singleions are easier to realize multi-wavelength laser due to their larger inhomogeneity of gain profile. However, so far results of the multi-wavelength Yb-doped fiber laser have not been reported. In this paper, development of an Yb-doped fiber ring laser with this type of filter is presented. In the ring cavity we use a section of standard single-mode optical fiber (cutoff wavelength of 1260 nm) as "multimode fiber" for the 1030-nm region. By adjusting the light's polarization state, a multi-wavelength laser emission along the amplification band of the Yb 3ϩ ion of about 1030 nm is obtained at room temperature.To the best of our knowledge, this is the first paper related to the multi-wavelength of the Yb-doped fiber laser and to the multiwavelengths in the region of 1030 nm which should result in contributions to the optical spectrum. Figure 1 shows the configuration of the laser. The active medium is 7 m of 560 ppm Yb 3ϩ -doped single-mode fiber with a numerical aperture of 0.14, a core diameter of 5.05 m, and a cutoff wavelength of 910 nm. The Yb-doped fiber is pumped by a 976-nm laser diode with a maximum power of 60 mW through a 980/ 1060-nm wavelength division multiplexing (WDM) fiber coupler. The coupling efficiency of the WDM fiber coupler is approximately 90% at the lasing wavelength. And a 45:55 coupler of 1060 nm is used as the output coupler. A section of 4.5-m G.652 fiber, whose cutoff wavelength is 1260 nm and V ϭ 2.942 for the 1030-nm laser, is fusion spliced into the fiber cavity. LP 01 and LP 11 modes are excited into the G.652 fiber, so it can be used as a section of "multimode" fiber for laser light. Thus, the combined fibers are used as a spatial mode-beating filter to generate multiwavelength lasers. A polarization controller (PC) twined by the G.652 fiber is used to control the position and the number of wavelength peaks in the laser-output spectrum. The output laser is measured with an optical spectrum analyzer (ADVANTEST Q8383). EXPERIMENTAL SETUP EXPERIMENTAL RESULTS AND DISCUSSIONWhen pump power is increased to 22.5 mW (PC fixed in some state), a light with wavelength of 1036.2 nm at first preferentially lases and then keeps stable for a long time. When pump power is increased, more wavelengths will lase. The lasing wavelengths are located in the range of 1025.6 ϳ 1046.6 nm. The line width of every wavelength laser is about 0.16 nm, and the side-modesuppression ration (SMSR) is about 40 dB. The smallest peak space obtained is 1.3 nm. Figure 2 shows the two stable wavelengths with peak spacing of 5.2 nm. Repeated scanning results indicate that the wavelength spacing holds stable and there are slight power fluctuations among the longitudinal modes. When the two wavelengths are working, peak spaces from 1.3 nm to 13 nm can be obtained. And the power of each wavelength is about 3 mW. By precisely controlling the states of PC, the...

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